1. Field of the Invention
The present invention relates to a method for conducting film coating on the surface of spinning circular workpiece under the action of gas pressure and a nozzle utilized in the same, more particularly to a novel technology of uniformly coating a film having nano-scale thickness on the surface of circular workpiece.
2. Brief Description of the Prior Art
So far, there are substantially two methods of coating polymer solution on the surface of circular workpiece, one is spray coating method and the other one is blade coating method.
In the spray coating method, polymer solution (for example, photoresist, UV resin) is firstly filled in spray gun, and then the polymer solution is atomized into mist droplets after passing through the spray gun, in turn the mist droplets is sprayed by high-pressure gas onto the surface of a circular workpiece so as to finish the coating of the circular workpiece. However, in the spray coating method, the outlet pressure of spray gun has a Gaussian distribution (clustering around center and is thin outside the center), hence mist droplets is failed to be uniformly distributed especially when the mist droplets is in nano-scale size. Therefore, the spray coating method cannot produce polymer film having highly uniform thickness below 1 μm.
Referring to FIG. 13, the blade coating method is essentially to use a doctor blade (7) to wipe redundant polymer solution (9) off the surface of the circular workpiece (8), and the thickness of the polymer solution coating is determined by adjusting the gap between the doctor blade (7) and the circular workpiece (8). The method of wiping off redundant polymer solution (9) by the doctor blade (7) can reach certain extent of uniformity in the blade coating technology, but the doctor blade (7) usually in mechanical feeding can hardly reach a distance of less than 10 μm from the surface of circular workpiece, let alone a displacement precision of 1 μm. Hence, a film of polymer solution having thickness less than 1 μm cannot be achieved by the blade coating method. Moreover, adhesion of the doctor blade (7) on the coated film is often occurred during separation from the circular workpiece (8) such that bad roundness is caused.